Continuous epitaxial deposition system

ABSTRACT

An epitaxial deposition system includes slice transporting boats which index individual slices between work stations. At the work stations, the temperature of the slices is controlled and the boats are sequentially filled with various gases, including an etching gas and a deposition gas. The work stations are surrounded by a sealed enclosure which receives gases discharged from the boats.

United States Patent [72] Inventor Warren Rice Tempe, Ariz.

[2i] Appl. No. 850,015

[22] Filed Aug. I4, 1969 [45] Patented Aug. 10, 1971 [73] Assignee TexasInstruments Incorporated Dallas, Tex.

[S4] CONTINUOUS EPITAXIAL DEPOSITION SYSTEM 6 Claims, 2 Drawing Figs.

(52] U.S.Cl 118/48 C23c 11/00 Field of Search 118/48- [56] ReferencesCited UNITED STATES PATENTS 2,674,809 4/1954 Meienhofer 2l9/388 UX3,190,262 6/ l 965 Bakish et al. l 18/48 3,473,5 l0 l0/l969 Sheng et al.l 18/495 Primary Examiner-Morris Kaplan Attorneys-James 0. Dixon, AndrewM. Hassell, Harold Levine, Melvin Sharp, John E. Vanidgrifl, Henry T.Olsen and Michael A. Sileo, Jr.

ABSTRACT: An epitaxial deposition system includes slice transportingboats which index individual slices between work stations. At the workstations, the temperature. of the slices is controlled and the boats aresequentially filled with various gases, including an etching gas and adeposition gas. The work stations are surrounded by a sealed enclosurewhich receives gases discharged from the boats.

PATENTEDAUBIOISTI 3,598,082

FIG. I

INVENTORI WARREN RICE ATTORNEY CONTINUOUS EPITAXIAL DEPOSITION SYSTEM Inthe electronic component manufacturingindustry, certain products areproduced by processes in which epitaxial layers are deposited onsubstrate slices. l-leretofore, most epitaxial deposition processes havebeen designed to form layers on a large number of slices at the sametime. This practice is known as batch processing.

Batch processing has several inherent disadvantages. First, in order toreduce the cost of each layer, batch processing is usually carried outin relatively large chambers. Deposition chambers must be purged andheated before the start of each deposition process. When large chambersare employed, the

' purging and heating procedure requires a relatively long time.

Second, it is very difficult to heat all portions of a large chamberuniformly. Also, it is difitcult to supply deposition gas to a largenumber of slices on a unifonn basis. irregularities in slice. heatingand exposure to deposition gas result in differences between theepitaxial layers that are formed on various slices.

This invention relates to an epitaxial deposition system'that operateson a continuous basis. The system operates on each slice in exactly thesame way. Use of the system results in the fabrication of extremelyuniform epitaxial layers.

ln the preferred embodiment of the invention, epitaxial layers areformed on substrate slices by discharging a plurality of gases, at leastone of which is a deposition gas, and by sequentially moving each sliceinto engagement with each gas. Preferably, the slices are positioned inboats and are engaged with the gases by sequentially filling the boatswith each of the gases.

A more complete understanding of the invention may be had by referringto the following detailed description when taken in conjunction with thedrawing, wherein:

FIG. 1 is a side view of a deposition system employing the invention inwhich certain parts have been broken away and certain parts have beenshown schematically more clearly to illustrate certain features of theinvention, and

FIG. 2 is an illustration of a slice transporting boat useful in thepractice of the invention.

Referring now to the drawing and particularly to FIG. 1 thereof, thereis shown a deposition system employing the invention. The system 10includes a plurality of work stations A, B, C, D, and E and a pluralityof boats 12 which are employed to transport substrate slices between thework stations. As the slices are transported between the work stations,the system 10 operates to form epitaxial layers on the substrates. Thesystem 10 operates on a continuous basis in that an epitaxial layer isfonned on each substrate sliceautomatically as the slice is transportedbetween the work stations by one of the boats 12.

Referring now to FIG. 2, the structural details of the boats 12 areshown. Each boat 12 is formed from quartz and includes a flat floor l4and an upper portion 16 which may be of any convenient shape. One end ofthe upper portion 16 is closed. The other end is open to permit slicesto be positioned within and removed from the boat. An inductionsusceptor l8 comprised of a silicon carbide coated graphite cylinder ispositioned on the floor 14. in use, a slice is positioned on thesusceptor 18 of each boat 12 for transportation through the system 10.

The boats 12 each include a gas inlet hole 20. The hole 20 is formed inthe floor 14 and extends to a mixing chamber which is separated from theremainder of the boat 12 by a wall 22. The wall 22 has a slot 24 formedthrough it which directs gas from the mixing chamber over the susceptor18. A gas outlet hole 26 is formed through the upper portion 16 of eachboat 12.

Referring now to FIG. 1, the boats 12 are moved between the stations A,B, C, D, and E in trainlike fashion. The boats 12 are positioned indirect contact with each other in the train so that the closed end ofone boat 12 operates to seal the open end of the next adjacent boat. Thetrain of boats is preferably moved through the system 10 by an indexingmechanism (not shown) which advances the train one boat length each timeit is actuated. By'this means, each boat 12 is sequentially indexed intoengagement with each work station of the system l0.

The deposition system 10 includes an enclosure 28 which extends overallof the work stations of the'system. The enclo sure 28 is formed fromquartz and includes a flat floor 30 over which the boats 12 travel asthey are indexed between the work stations. The enclosure 28 alsoincludes an upper member 32 comprising an enlarged central portion 34having a vent 36 formed in it and reduced end portions 38.

The end portions 38 of the enclosure 28 have-interior dimensionssubstantially identical to the exterior dimensions of the upper portions16 of the boats 12. Nitrogen (N is continually forced out of the ends ofthe enclosure 28 between the end portions 38 and the boats. The flow ofnitrogen between the end portions 38 and the boats 12 seals the interiorof the enclosure 28 against the entry of air.

Work station A includes a plurality of passageways 40 and a deliverytube 42. A coolant such as water is continually circulated through thepassageways 40 to maintain station A at a relatively low temperature.The delivery tube 42 extends through the floor 30 of the enclosure 28and is connected to a source of nitrogen (N,).

As each boat 12 is indexed to station A, the gas inlet hole 20 formed inthe floor 14 of the boat is brought into alignment with the upper end ofthe delivery tube 42. Nitrogen flows into the boat 12 from the deliverytube 42 to purge the interior of the boat of air. Air from the boat, andsubsequently nitrogen from the tube 42 flows out of the gas outlet hole26 formed in the upper portion 16 of the boat 12 into the centralportion 34 of the enclosure 28. From the enclosure 28 the air andnitrogen flow out of the system 10 through the vent 36.'While the boat12 is at work station A it is maintained at a reduced temperature by theflow of coolant through the passageways 40. a

Work station B includes a heating device 44 and a delivery tube 46. Theheating device 44 comprises a'pancake type induction heating coil thatis connected to a suitable source of induction heating power. Thedelivery tube 46 extends through the floor 30 of the enclosure 28 and isconnected to a source of hydrogen (H and to a source of hydrogenchloride As each boat is indexed to work station B, the heating device44 immediately begins to increase the temperature of the interior of theboat. As the temperature of the boat is raised, hydrogen is fed into theinterior of the boat 12 through the delivery tube 46 to further purgethe boat of air. Subsequently, either pure hydrogen chloride, hydrogen,or a mixture of the two is fed into the interior of the boat 12. Theslot 24 formed in the wall 22 of the boat 12 directs the hydrogenchloride over the upper surface of a slice positioned on the inductionsusceptor 18. The hydrogen chloride etches the surface of the slice torender the surface absolutely clean.

Work station C is the epitaxial deposition station of the system 10.Station C includes a heating device 48 comprised of a pancake typeinduction heating coil and a suitable source of induction heating power.Station C also includes a delivery tube 50 which extends through thefloor 30 of the enclosure 28 and which is connected to a source ofdeposition gas.

Before a boat 12 is indexed to Station C, the temperature of the slicepositioned on the susceptor 18 of the boat is raised to a temperaturesuitable for epitaxial deposition by the heating device 44 of theStation B. At station C, the slice is maintained at the depositiontemperature by the heating device 48. The delivery tube 50 directs adeposition gas into the interior of the boat 12 through the gas inlethole 20. In the boat l2, the slot 24 directs the deposition gas over theslice positioned on the susceptor 18. As the gas engages the heatedslice, an epitaxial layer is formed on the slice.

The nature of the deposition gas that is supplied to the boats 12through the tube 50 depends upon the nature of the epitaxial layer to beformed. Ordinarily, the deposition gas will be comprised of a mixture ofvarious gases. For example, if a silicon epitaxial layer is to beformed, the deposition gas may inelude silicon tetrachloride (SiClhydrogen (H,) and an appropriate donor gas such as dibrane, arsine,phosphine, etc. depending upon the type of doping desired.

When the deposition of an epitaxial layer on the slice contained in aboat 12 has been completed, the boat is indexed to work station D.Station D includes a plurality of coolant passageways 52 and a deliverytube 54. The tube 54 extends through the floor 30 of the enclosure 28and is connected to a source of hydrogen (H .At work station D, eachboat 12 is cooled by the flow of a coolant such as water through thepassageways 52. Simultaneous ly, hydrogen is fed into the interior ofthe boat throughthe tube 54 and the hole 20. The hydrogen forces thedeposition gas out of the boat 12 and thereby stops the depositionprocess.

Work station E includes a delivery tube 56 which is connected to asource of nitrogen (N,). At work station E, nitrogen is introduced intothe interior of the boat 12 through the tube 56. The nitrogen purges theboat 12 of the hydrogen that was introduced into the boat at the stationD. The nitrogen also further reduces the temperature of the interior ofthe boat.

it should be understood that while the boats 12 are positioned at eachof the work stations A, B, C, D, and E, the delivery tubes at the workstation cause the various gases employed in the system to flow throughthe boats 12 on a con tinuous basis. That is, while a boat is at eachwork station, a gas continuously flows through the inlet hole 20,through the 'slot 24, and through the outlet hole 26 of the boat. Thegases flowing from the outlet holes 26 of the boats 12 merge together inthe enlarged central portion 34 of the enclosure 28 v and flow throughthe vent 36 of the enclosure 28 combined state. Thus, the boats 12 notonly transport slices between the various work stations of the system10, but also prevent unintentional contact between the slices and thevarious gases em ployed in the system.

it should be understood that the deposition system illustrated in thedrawing is a basic system and that many modifications to the system arepossible, For example, in many systems, additional stations identical tothe work station B will be provided to assure proper slice preheatingbefore the beginning of epitaxial deposition. In such a case, hydrogenchloride will ordinarily only be supplied to the boats at the last typeB work station.

Similarly, in many systems more than one type C work station will beprovided. in such systems, a portion of the epitaxial deposition processis carried on at each such work station.

Finally, in many systems it will be desirable to provide additional workstations similar to the station C at which different deposition gasesare directed over the heated slices. In such systems multiple epitaxiallayers of different types are formed on each slice as it passes throughthe system.

of course, the structural details of the work stations comprising thesystem 10 are illustrated by way of example only and may be freelysubstituted. For example, heat pipes can be employed in the workstations B and C instead of induction heating coils. In such a case,either induction type or resistance type heating elements can beutilized in heating the heat pipes. Similarly, the work stations A and Bcan be cooled by heat pipes connected between the work stations andsuitable heat sink.

Like the structural details of the work stations, the structural details'of the boat 12 of the system 10 can be varied to provide specificperformance characteristics in the system. For example, it has beenfound that many deposition gases do not react properly with slicesurfaces when the surfaces are positioned exactly horizontally.Accordingly, in many systems it is desirable to position the workstations along an upwardlyextending" plane so that the boats 12 travelangularly upwardly through the system 10. In such a case, the boats 12may advantageously be equipped with suitable baffles and outlet holesto'guide the various gases employed in system 10 with respect to theslices contained in the boats.

In some systems, induction susceptors will not provide adequate heattransfer to the slices. In such a case, heat pipes can be substitutedfor the susceptors in the boats. When heat pipes are employed they canoften be formed integrally with the boat structure. I

in many systems, radiation losses through the upper. portions of theboats will be considerable. To this end, it will often be desirable toprovide a radiation shield in each boat. This can be accomplished byforming the upper portion of each boat from two layers of quartz andpositioning a layer of metal between the quartz layers. When such alayer of metal is enclosed in an inert gas atmosphere, it assumes a highand stable temperature and thereby minimizes radiation losses from theslice contained in the boat.

The epitaxial deposition system illustratedin the drawing differs fromprior systems principally in that it is a continuous process. Thus, eachwork station of the system operates on a steady state basis. And, theboats are indexed at the end of equal time intervals to transport slicesbetween the stations.

The continuous nature of the system results in distinct advantages overprior systems. For example, because the heating devices of the systemare operated continuously and because the boats locate each slice onexactly the same position with respect to the heating devices, thesystem provides extremely uniform slice heating. That is, every slice isheated at the same rate and to the same temperature as every otherslice.

The continuous nature of the system also results in more uniform gasflow than has been possible heretofore. The various gases employed inthe system are continuously supplied to their respective delivery tubesat the same temperature and pressure. insofar as possible, the boats ofthe system are constructed exactly alike. Therefore, the gas supplied ateach work station of the system flows through each boat in exactly thesame manner.

The advantages of the continuous nature of the system may be summarizedsimply; every slice is treated alike. That is, because of the uniformslice heating and gas flow characteristics of the system, the epitaxiallayer that is deposited on one slice is the same as the layer depositedon any other slice. Thus, the use of the system results in an extremelyuniform product.

in addition to being continuous, the epitaxial deposition systemillustrated in the drawings is superior to prior systems because it issequential. That is, slices emerge from the system in exactly the sameorder in which they are introduced. Sequential operation permits theresults of changes in the operational parameters of the systems to bemore easily traced. Also, in the event that the system fails to producea satisfactory product, the cause of the failure is more easilydetermined. 7

Although only one embodiment of the invention is illustrated in thedrawing and described hereing it will be undetstood that the inventionis not limited to the embodiment disclosed but is capable ofmodification, rearrangement and substitution of parts and elementswithout departing from the spirit of the invention.

l. A deposition system comprising:

a. means for discharging a plurality of selected gases into a pluralityof work stations;

b. a plurality of boats and means for sequentially moving said boatsinto said work stations, each boat having at least first and secondcompartments, such that said selected gases sequentially flow throughsaid first and second compartments; and

c. means for maintaining said boats and work stations at predeterminedtemperatures.

2. A deposition system in accordance with claim I in which each of saidboats has a substantially flat bottom portion, a curved top portionjoining said bottom portion along two edges, one substantially flat endportion joining said bottom and curved top portion thereby closing oneend of said boat and a partition having an opening therein joining saidbottom and top portions thereby dividing said boat into twocompartments.

3 A deposition system in accordance with claim 1 which includes at leastone work station having tubes through which a coolant may be circulatedto reduce the temperature by said work station and a boat positionedtherein.

4. A deposition system in accordance with claim 1 which includes atleast one work station having heaters which may be used to increase thetemperature of said work station and a boat positioned therein.

5. A deposition system in accordance with claim 1 in which each of saidboats includes a susceptor on which a semiconduetor slice may be placedand heated by induction heating.

' 6. A deposition system in accordance with claim I wherein said boatsmove in trainlike fashion into and through said work stations, such thatthe closed end of each of said boats is positioned adjacent to the openend by a following boat thereby closing said open end by said followingboat.

1. A deposition system comprising: a. means for discharging a pluralityof selected gases into a plurality of work stations; b. a plurality ofboats and means for sequentially moving said boats into said workstations, each boat having at least first and second compartments, suchthat said selected gases sequentially flow through said first and secondcompartments; and c. means for maintaining said boats and work stationsat predetermined temperatures.
 2. A deposition system in accordance withclaim 1 in which each of said boats has a substantially flat bottomportion, a curved top portion joining said bottom portion along twoedges, one substantially flat end portion joining said bottom and curvedtop portion thereby closing one end of said boat and a partition havingan opening therein joining said bottom and top portions thereby dividingsaid boat into two compartments.
 3. A deposition system in accordancewith claim 1 which includes at least one work station having tubesthrough which a coolant may be circulated to reduce the temperature bysaid work station and a boat positioned therein.
 4. A deposition systemin accordance with claim 1 which includes at least one work stationhaving heaters which may be used to increase the temperature of saidwork station and a boat positioned therein.
 5. A deposition system inaccordance with claim 1 in which each of said boats includes a susceptoron which a semiconductor slice may be placed and heated by inductionheating.
 6. A deposition system in accordance with claim 1 wherein saidboats move in trainlike fashion into and through said work stations,such that the closed end of each of said boats is positioned adjacent tothe open end by a following boat thereby closing said open end by saidfollowing boat.